Cyanate has been shown to be an active-site-directed inhibitor of carbamyl phosphate synthetase from Escherichia coli. Preliminary studies and one published report indicate that cyanate also specifically inhibits at least four other amidotransferases, apparently by carbamylating a functional group at the glutamine binding site. With respect to these interactions, the studies which are proposed include 1) elucidating the detailed properties of the interaction of cyanate with purified preparations of the enzymes glutamate synthetase, cytidine triphosphate synthetase, and a glutamine- and N-acetyl-L-glutamate-dependent carbamyl phosphate synthetase from fish, 2) investigating in more detail the interaction of cyanate with carbamyl phosphate synthetase from E. coli, 3) correlating these studies to obtain information about the relationship between the glutamine binding site and the remainder of the active site of each amidotransferase and about the general mechanism of ammonia transfer, and 4) correlating these studies to obtain information about the properties and mechanism of action of carbamyl phosphate synthetases. Kinetic studies designed to obtain information about the mechanism of the catalytic mechanism of carbamyl phosphate synthetase are in progress. The enzyme cyanase is currently being isolated from Escherichia coli and the biological role of this enzyme is under investigation.